Generally, methods for jointing metals to one another can be classified into the fusion welding with which the materials to be jointed are fused to be jointed; the pressure welding with which the materials to be jointed are kept as a solid, but jointed by diffusion of the metal atoms; the brazing with which the materials to be jointed are kept as a solid, but jointed through another material for brazing; and the adhesion with which an adhesive is used for jointing the materials.
Here, there will be a discussion about bonding of a fine diameter wire in manufacturing of electronic components. With the high-performance miniaturization of electronic equipment, miniaturization and high-density packaging of electronic components have been progressed, and this trend has caused a demand for highly reliable and sophisticated bonding techniques. For bonding of small-sized components, such as the above-mentioned electronic components, soldering (belonging to the category of brazing), ultrasonic welding or resistance welding (both belonging to the category of pressure welding), or adhesion are being used.
Conventionally, as methods for determining acceptance/rejection of such a minute metal bonding portion by conducting a test after the bonding, the method by visual inspection (Japanese Unexamined Patent Application Publication No. Hei 7-190992, and the like); the method by image processing (Japanese Unexamined Patent Application Publication No. 2001-60605, and the like); the method by appearance observation, making evaluation by X-ray radiographic test, or the like (Japanese Unexamined Patent Application Publication No. Hei 9-80000, and the like); the method by power-on test (Japanese Unexamined Patent Application Publication No. 2006-35237, and the like); the method by tensile test (Japanese Unexamined Patent Application Publication No. Hei 7-235576, and the like); the method by non-appearance observation, making evaluation on the basis of heat distribution, or the like (Japanese Unexamined Patent Application Publication No. 2001-215187, and the like); and the like, are known.
However, the above-mentioned evaluation method by visual inspection is a method by microscope observation, and therefore, inspection by a skilled craftsman can be expected, however, it involves a large individual difference, presenting problems in points of uniformity in quality and recruitment, and the evaluation method by image processing is a method which makes computer image processing to determine acceptance/rejection on the basis of the position or appearance geometry, and it can be automated, however, with it, there is a problem that evaluating the bonding state to determine acceptance/rejection on the basis of the appearance is considerably difficult.
Further, the evaluation method by conducting an X-ray radiographic test is a method of determining acceptance/rejection of the bonding state on the basis of the X-ray radiographic test, and it allows the bonding portion to be directly observed, however, it presents such a problem as that, in order to evaluate the bonding portion for determining acceptance/rejection, still higher resolving power is required. In addition, the evaluation method by conducting a power-on test is a method which actually conducts a power-on operation test, and it has a high reliability, but in order to determine acceptance/rejection of the bonding state, it is fundamentally required to pass a large current for evaluation, and thus this method is not a realistic one.
Furthermore, the evaluation method by conducting a tensile test is a method which tests the tensile strength, and it has a high reliability, but involves a destructive inspection, thus presenting a problem that it is impossible to make a total inspection. The evaluation method on the heat distribution allows inspection to be made non-destructively, however, it presents many problems, such as that about correlation between the heat distribution and the bonding state, and that a practicable two-dimensional heat sensor is expensive.